The present invention relates generally to an improved composite material. More specifically, the present invention relates to a thermally and electrically conductive composite material that is net-shape moldable and easily moldable or castable.
In the heat sink industries, it has been well known to employ metallic materials for thermal and electrical conductivity applications, such as heat dissipation for cooling semiconductor device packages, grounding and electrical signal transmission. For these applications, such as thermally conductive heat sinks, the metallic material typically is tooled or machined from bulk metals into the desired configuration. However, such metallic conductive articles are typically very heavy, costly to machine and are susceptible to corrosion. Further, the geometries of machined metallic heat dissipating articles are very limited to the inherent limitations associated with the machining or tooling process. As a result, the requirement of use of metallic materials which are machined into the desired form, place severe limitations on heat sink design particular when it is known that certain geometries, simply by virtue of their design, would realize better efficiency but are not attainable due to the limitations in machining metallic articles. In addition, electrically conductive members suffer from the same disadvantages in that they are also difficult to form into the desired configuration.
It is widely known in the prior art that improving the overall geometry of a heat dissipating or electrical transmitting article, can greatly enhance the overall performance of the article even if the material is the same. Therefore, the need for improved article geometries necessitated an alternative to the machining of bulk metallic materials to provide thermal and electrical transfer. To meet this need, attempts have been made in the prior art to provide molded compositions that include conductive filler material therein to provide the necessary thermal conductivity. The ability to mold a conductive composite enabled the design of more complex part geometries to realize improved thermal and electrical performance of the part.
The attempts in the prior art included the employment of a polymer base matrix loaded with a granular material, such as boron nitride grains. Also, attempts have been made to provide a polymer base matrix loaded with flake-like filler material. These attempts are, indeed, moldable into complex geometries but still do not approach the desired performance levels found in metallic machined parts. In addition, known conductive plastic materials are undesirable because they are typically very expensive to manufacture because they employ very expensive filler materials. Still further, these conductive composite materials must be molded with extreme precision due to concerns of filler alignment during the molding process. Even with precision molding and design, inherent problems of fluid turbulence, collisions with the mold due to complex product geometries make it impossible to position the filler ideally thus causing the composition to perform far less than desirable.
Moreover, the entire matrix of the composition must be satisfactory because heat transfer is a bulk property rather than a direct path property such as the transfer of electricity. Heat is transferred in bulk where the entire volume of the body is employed for the transfer while a direct path is needed to conduct electricity. Therefore, even if a highly conductive narrow conduit is provided through a much lower conductive body, the heat transfer would not be as good as a body which is consistently marginally conductive throughout the entire body. Therefore, consistency of the thermal conductivity of the entire matrix of the composite body is essential for overall high thermal conductivity. Also, direct paths are required to achieve efficient electrical conductivity.
In view of the foregoing, there is a demand for a composite material that is highly thermally conductive and/or electrically conductive. In addition, there is a demand for a composite material that can be molded or cast into complex product geometries. There is also a demand for such a moldable article that exhibits thermal and/or electrical conductivity as close as possible to purely metallic conductive materials while being relatively low in cost to manufacture.